Conventional digital communications systems, such as systems that practice the IS-95 communication standard, transmit communication signals between a base station and handset receivers. In such systems, many different base stations are located in geographically diverse locations. Each base station therefore covers a portion of the overall area in which communications can occur. In order to increase overall capacity, the area covered by a single base station, typically known as a cell, will have reduced size, or different cells will overlap.
In operation, conventional systems transmit communications signals from the base station to the terminal device using certain communication bands, collectively known as either the downlink or the forward link. Also such conventional systems transmit communications signals from the terminal device to the base station using other communication bands, collectively known as the uplink or reverse link. In such systems, recovery of communications on the reverse link is more difficult than recovery of communications on the forward link, since communications from many different terminal devices must be simultaneously detected from a single received signal at a base station.
To help assist with the simultaneous detection of signals from different terminal devices on the reverse link, such conventional digital communications systems use power control in order to reduce interference for terminal devices that are at different distances within a particular cell. IS-95 describes a particular power control scheme, which effectively maintains the power of multiple terminal devices at different distances at levels such that each terminal device can communicate without interference from other terminal devices predominating. Accordingly, with such a power control scheme, higher transmit power is used for longer range.
Another type of digital communication system is of the type described in the 802.11 Wireless LAN standard. With this standard, there are two ISM bands intended for communications, 902-928 MHz and 2.4-2.48 GHz, and each band has different maximum transmit power levels associated with it. As originally envisioned, digital communication systems that implement this standard use a carrier-sensing multiple access scheme, such that there can be only one device transmitting at a time. The different maximum transmit power levels associated with each band are used to accommodate different ranging requirements.
While these systems have allowed digital communications to evolve, they have their drawbacks. One such drawback is that the data rate for each terminal device is maintained at some nominal rate, regardless and independent of the power being used.
Recently the FCC allocated three bands in the 5 GHz range, the U-NII bands 5.15-5.25 GHz, 5.25-5.35 GHz, and 5.725-5.825 GHz, for general use in wireless communication. More effective use of bandwidth for devices operating in these bands would allow for more efficient communications. Specifically, rather than specifying a certain maximum data rate for all devices, it would be desirable to have variable data rates for different devices operating within these bands, such that all of the devices need not have a maximum data rate, but could use various amounts of the overall bandwidth, depending upon the power that each device was using. Thus, in contrast to conventional digital communications systems that do not allow for any trade-offs to occur between capacity and distance, it would be desirable to have a system that allows for increases in capacity if each terminal device were operating closer to the intended receiver, and thereby using less power.